Four boys named Haruka, Makoto, Nagisa and Rin all participated in a swimming tournament shortly before graduating elementary school and later parted ways. Years later, they reunite when Rin challenges Haruka to a race and wins. Not wanting to be defeated so easily, Haruka gathers Makoto and Nagisa and a new recruit named Rei to form the Iwatobi High School Swimming Club.
The boys of summer are back. Haru, Makoto, Nagisa, Rei, and Rin are reunited and the competition is about to get fierce. After the last swimming meet, the bonds of friendship have only gotten stronger, and with each passing day the boys continue to grow. This summer brings new rivals and new challenges.